Field of the Invention
The invention is directed to composition and in vivo and ex vivo methods for organ protection. In particular, some of the compositions and methods are used in vivo to treat or prevent ischemic injury to organs, and some of the compositions and methods are used ex vivo to treat or prevent damage to harvested organs.
Prior Art
Deaths due to injury in the US reached over 190,000 and costs over $400 billion a year in health care costs and lost productivity in 20121. Deaths from trauma are the number 1 cause of death for people under 44 years of age in the US and the third leading cause of death overall for all age groups. Trauma accounts for about 30% of all life years lost in the US, compared to cancer (16%), heart disease (12%), and HIV (2%)2. For all traumatic injuries, hemorrhagic shock is responsible for over 35% of pre-hospital deaths and over 40% of all deaths within the first 24 hours. This is second only to trauma deaths induced by severe CNS injury3. Finally, hemorrhagic hypotension exposes the patient to immediate complications of life threatening infections, coagulopathies, and multiple organ failure4,5.
Initial therapy of trauma and hemorrhage shock centers on effective cessation of bleeding and on the infusion of large volumes (2 to 8 liters) to replace lost blood volume. This is considered necessary to restore normal circulatory functions such as arterial blood pressure, cardiac output, oxygen consumption and renal function. Conventionally, isotonic fluids are used for high volume resuscitation. Many cellular complications and practical limitations have been cited while using high volume fluids for resuscitation. When blood is lost, the greatest immediate need is to stop further blood loss, but the second greatest need is replacing the lost volume. If the fluid volume is maintained, remaining red blood cells may still be sufficient to circulate and oxygenate body tissues for a period of time. In this scenario, it may be possible to reduce or prevent ischemic injury if appropriate medical or surgical intervention can be accomplished.
Recently, resuscitation of hemorrhaged animals and injured patients has been performed with low volume hyperosmotic saline solutions with little success. Glucose or mannitol has been tested with less successful results. Small volume resuscitation has been successfully used in some cases using hyperoncotic albumins or high molecular weight tense state polymerized hemoglobins. The use of hypertonic saline solutions (HTS) or colloid solutions (albumin, HES, Hetastarch, Hextend) have had very limited success in clinical trauma and resuscitation, and, due to their mechanism of action, they do not prevent cell swelling. Crystalloids are available for pre-hospital use because they can be safely transported and stored but they are generally limited in their effectiveness. Attempts to modify basic intravenous crystalloids for pre-hospital resuscitation by adding hypertonic NaCl or starch (Hextend) as a volume expander have had disappointing results6, 7. The future use of effective spray dried blood products will be a valuable tool in pre-hospital settings since they replace chemical coagulation precursors and factors. The use of fresh frozen plasma in the field, which is currently being tested at many centers, will also be useful but it too is limited by the need for refrigeration8.
However, none of these procedures is known to be effective in preventing lethal cell swelling in vivo. Cells, organs, and tissues that suffer from lack of oxygen delivery, as occurs during traumatic shock and hemorrhagic hypovolemia, begin to swell with water because they lose energy dependent volume control mechanisms. In patients suffering from acute hemorrhagic shock and/or trauma, there is substantial intracellular oxygen deprivation, which in turn drops ATP concentration. Due to lack of ATP, the cellular sodium pump fails and free sodium enters the cell, followed by osmotic water movement. Movement of water into the cell causes swelling that leads to organ failure and death. Massive cell swelling further compresses the capillaries and sinusoids and impedes microcirculatory flow through organs and tissues even when the blood pressure is restored after hemorrhage. This is called the “no reflow phenomenon” and it occurs largely from local cell swelling.
This is particularly a problem in battlefield or civilian pre-hospital settings where large volumes cannot be carried and administered to patients in need of rapid paramedical intervention and transport to hospital or surgical treatment centers. There is a so-called “golden hour” of time during which restoration of blood volume and prevention of ischemic injury must be achieved to prevent catastrophic organ failure and death. There is no present day technology to deal with cell swelling and tissue damage to patients experiencing prolonged periods of shock and low volume resuscitation.
In addition, the treatment of choice for patients in end-stage heart failure is heart transplantation. Donor heart availability limits the use of this procedure and has given birth to new mechanical assist or replacement devices that are generally intended to bridge patients to heart transplantation by allowing them to survive on longer wait lists. While this approach works, the availability of more hearts would be welcome. These new hearts would likely enter the donor pool by expanding the current donor criteria and accepting hearts that are injured from warm ischemia (donation after cardiac death, DCD). However, these hearts are currently considered to be unusable and need to be reconditioned to improve function (reanimated) before they can be considered acceptable as transplantable donor organs.
Mechanisms of reanimation have focused on repair and replacement of severely damaged mitochondria in cardiomyocytes from DCD hearts because mitochondrial death is the most likely causative event in DCD heart dysfunction, based on preliminary data in human DCD heart recovery. A prolonged ex-vivo perfusion period between donor heart recovery and transplantation is required to affect mitochondrial repair or replacement through biogenesis. It may be possible to affect mitochondrial biogenesis (replacement) provided the reanimation period is long enough and provided the heart's metabolic needs can be maintained during that period. During this repair period, the myocardium must be adequately perfused. Currently, this is not possible because stable perfusion of the myocardium ex-vivo with existing perfusion preservation solutions (MPS) do not work. Typically, tissue edema and metabolic cell swelling occur early in heart perfusion, which limits adequate tissue oxygen delivery over the prolonged times that are needed for repair.
There is a need for improved compositions and methods to lengthen the time available between organ donation and transplantation, and also to permit time for compromised organs to regain functionality prior to transplant.